1 Musculoskeletal MRI: Practical Protocols Timothy J. Mosher, MD Chief, Musculoskeletal Imaging and MRI Penn State University College of Medicine Hershey, PA Learning Objectives • Discuss general considerations in designing clinical MRI protocols • Understand the role of contrast resolution in the context of imaging connective tissues • Present clinical MRI protocols for MSK MRI at 3.0 T What is a “Practical” MRI Protocol • A practical protocol is not a perfect protocol • The final product must satisfy many different customers with competing interests • For every protocol there is a colleague with a better protocol Organizational Guidelines • Use detailed MRI requests and patient questionnaires to extract sufficient history – Mark site of tenderness/mass with fiducial marker • Use targeted MRI protocols – Primary objective – Secondary objective • Limit patient examination times to 45 minutes or less • Always perform the most important sequence first • Invest in education for technologists General Approach for Designing Clinical MRI Protocols 1. Obtain sufficient signal to noise (SNR) to get the job done 2. Optimize contrast for the tissue that you are evaluating 3. Select image plane and resolution based on the anatomy that you are evaluating 4. Adjust acquisition parameters to minimize artifact Signal to Noise Signal to Noise Signal: INCOME Noise: EXPENSE Resolution Contrast Speed
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1
Musculoskeletal MRI: Practical ProtocolsTimothy J. Mosher, MD
Chief, Musculoskeletal Imaging and MRIPenn State University College of Medicine
Hershey, PA
Learning Objectives
• Discuss general considerations in designing clinical MRI protocols
• Understand the role of contrast resolution in the context of imaging connective tissues
• Present clinical MRI protocols for MSK MRI at 3.0 T
What is a “Practical” MRI Protocol
• A practical protocol is not a perfect protocol• The final product must satisfy many different
customers with competing interests• For every protocol there is a colleague with a
better protocol
Organizational Guidelines
• Use detailed MRI requests and patient questionnaires to extract sufficient history– Mark site of tenderness/mass with fiducial marker
• Use targeted MRI protocols– Primary objective– Secondary objective
• Limit patient examination times to 45 minutes or less
• Always perform the most important sequence first
• Invest in education for technologists
General Approach for Designing Clinical MRI Protocols
1. Obtain sufficient signal to noise (SNR) to get the job done
2. Optimize contrast for the tissue that you are evaluating
3. Select image plane and resolution based on the anatomy that you are evaluating
4. Adjust acquisition parameters to minimize artifact
Signal to NoiseSignal to NoiseSignal: INCOME
Noise: EXPENSE
Resolution
Contrast Speed
2
Resolution
Contrast Speed
Stationary Applications
MSK
Neuro
(+/-) Pelvis
Non-Stationary Applications
Abdominal
Enhanced Exams
Cardiovascular Applications
MRA
Cardiac
Principle 1:Principle 1: Musculoskeletal MR imaging protocols are optimized for contrast resolution at the expense of imaging speed
– Image blurring– Magnetization transfer– High SAR
1.5 T Turbo Spin Echo PD-weighted
Gradient Echo
Slice
Phase
Read
Tx
Rx
Gradient Echo
• Advantages– Fast imaging times– 3D acquisitions are
feasible• Disadvantages
– Moderate image contrast
– Prone to artifact• Metal artifact
1.5 T Water Excited T1-weighted GRE
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Principle 2:Principle 2: First optimize contrast based on tissue type, then adjust resolution based on anatomy
MRI Contrast in MSK Imaging
Articular Cartilage
Menisci, Tendons and Ligaments
FatChanges with Maturation
Skeletal Muscle
Bone Marrow
Effect of collagen on tissue contrast
• Efficient spin-spin (T2) relaxation– Tissue T2 is inversely related to collagen
concentration– Tissue T1 is less dependent on collagen
concentration– Anisotropic arrangement of collagen fibrils produces
an orientation dependence of T2 (Magic angle effect)• Magnetization transfer
– Collagen is the dominant macromolecular component for magnetization transfer
Field Dependence of Relaxation Times
00.2
0.40.6
0.81
1.2
1.41.6
1.8
4T 1.5T
MuscleFatMarrowCartilage
05
101520253035404550
4T 1.5T
MuscleFatMarrowCartilageTendon
T1 (sec) T2 (ms)
Duewell SH. et al. Radiology 1995; 196:551-555Fullerton GD et al Radiology 1985; 155:433-435 (tendon)
Sequence Selection for MSK MRI
Soft tissues– Muscle/Fat/Bone
Marrow• T1 FSE• T2 FSE with fat
suppression• STIR
Connective Tissues– Menisci/Ligaments/
Tendons• T1 SE• T1 or PD FSE• PD FSE with fat
suppression
– Articular Cartilage• PD FSE with or without
fat suppression• Fat suppressed T1
spoiled gradient echo
Principle 3:Principle 3: In evaluation of connective tissue pathology tissue contrast will primarily be determined by:
Pulse Sequence
Echo Time
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How do tissue properties influence MRI contrast?
Mow VC, Procter CS, Kelly MA. Biomechanics of articular cartilage. In: Basic biomechanics of the locomotor system, Nordin M, Frankel VH eds., pp 31-58 Philadelphia Lea and Febiger.
Type II Collagen Matrix of Articular Cartilage
Effect of collagen on cartilage T2
T2 weighted MRI (7T) Cartilage T2 Map
Freeze Fracture
Birefringence
0 (min)
1 (max)
Polarized Light Microscopy
T2: 10 100 ms
Cartilage T2 Mapping
Inverse Correlation of Cartilage T2 and Polarized Light Microscopy
Courtesy of MT Nieminen, Beth Israel Deaconess Medical Center, Boston, MA
The Magic Angle Effect in evaluation of connective tissue
Xia Y, Moody JB, Alhadlaq H.Magn ResonMed 2002; 48:460-469.
B0
Bz = m/r3 • (3cosθ-1)
Orientation with B0C
arti
lage
T2
(ms)
0 55 90 145 18020
40
60
80
xx
xx
θ = 54.74o
xx xxxx x
xx
x
xx
xx
Collagen Fiber Orientation Orientation Dependence of T2
Dependence of Cartilage T2 on Collagen Fibril Orientation
B0
T2-weighted
Image
Magic Angle
Magic Angle Effect: Tendons
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Magic Angle Phenomenon Tailoring the MRI protocol for evaluation of connective tissues
• Most clinical MSK MRI requests are for evaluation of connective tissue pathology